1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for reporting channel state information of multi-channel in a wireless local area network system.
2. Related Art
With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
Institute of electrical and electronics, engineers (IEEE) 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to 540 Mbps or higher, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate.
With the widespread use of the WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing rate supported by the IEEE 802.11n. A next-generation WLAN system supporting a very high throughput (VHT) is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing rate of above 1 Gbps in a MAC service access point (SAP).
To effectively utilize a radio channel, the next-generation WLAN system supports multi user-multiple input multiple output (MU-MIMO) transmission in which a plurality of non-access point (AP) stations (STAs) concurrently access to a channel. According to the MU-MIMO transmission, an AP can transmit frames concurrently to one or more MIMO-paired STAs.
The AP and the plurality of MU-MIMO paired STAs may have different capabilities. In this case, a supportable bandwidth, modulation coding scheme (MCS), forward error correction (FEC), etc., may vary depending on a STA type, usage, channel environment, etc.
The next-generation WLAN system shall support not only MU-MIMO but also data transmission using a wider bandwidth in order to achieve a higher throughput. However, it may be difficult to ensure a contiguous wide frequency bandwidth in a limited frequency band. To solve this problem, a method in which non-contiguous frequency bands are aggregated and used as one channel may be taken into account. Data transmission using a channel obtained by aggregating the non-contiguous frequency bands needs to support MU-MIMO transmission. Therefore, a procedure for acquiring/announcing channel state information for MU-MIMO transmission needs to be taken into account.